1. Field of the Invention
The invention relates to simulation of a radio channel, particularly a radio channel of a CDMA radio system.
2. Description of the Related Art
When a radio frequency signal is transmitted from a transmitter to a receiver, the signal propagates in a radio channel along one or more paths having different signal phases and amplitudes, which causes fadings of different duration and strength in the signal. In addition, noise and interference caused by other transmitters interfere with the radio connection.
A radio channel can be tested either in real circumstances or by using a software or hardware radio channel simulator that simulates real circumstances. Tests performed in real circumstances are cumbersome, since tests performed outdoors, for example, are subject to uncontrollable phenomena, such as the weather and the time of the year, which change continuously. In addition, a test carried out in one environment (city A) is not totally valid in a second, corresponding environment (city B).
A simulator simulating a radio channel can be used very freely to simulate a radio channel. In a digital radio channel simulator, a channel is usually modelled with a FIR filter (Finite Impulse Response), which provides convolution between the channel model and an applied signal by weighting the signal, delayed by different delays, with channel coefficients, i.e. tap coefficients, and by summing the weighted signal components. A random number generator provides channel coefficients that emulate the statistical values of a real channel.
In simulation the dominant paths of a measured or generated channel are the most important. When the impulse response has a high magnitude, it is potentially a dominant path. For simulation purposes the paths are often identified by visual inspection such that high amplitude values are denoted as the dominant paths.
However, there are problems related to the channel models used in simulators. Noise in the impulse response of a channel is usually not estimated. High peaks in the impulse response estimate can be due to noise rather than a deterministic signal, but the prior art cannot distinguish between peaks of noise and peaks of a deterministic signal. Additionally, a lot of memory is usually needed for processing the paths in the impulse response estimate.